The sources, fate and impacts of microplastics in aquatic ecosystems.

In this study, natural manganese oxides (MnO _x ), an environmental material with high redox potential, were used as a promising low-cost oxidant to degrade the widely used dyestuff methylene blue (MB) in aqueous solution. Although the surface area of MnO _x was only 7.17 m ² g ⁻¹ , it performed well in the degradation of MB with a removal percentage of 85.6% at pH 4. It was found that MB was chemically degraded in a low-pH reaction system and the degradation efficiency correlated negatively with the pH value (4–8) and initial concentration of MB (10–50 mg l ⁻¹ ), but positively with the dosage of MnO _x (1–5 g l ⁻¹ ). The degradation of MB fitted well with the second-order kinetics. Mathematical models were also built for the correlation of the kinetic constants with the pH value, the initial concentration of MB and the dosage of MnO _x . Furthermore, several transformation products of MB were identified with HPLC-MS, which was linked with the bond energy theory to reveal that the degradation was initiated with demethylation.

Gabapentin (GAB) is an emerging contaminant that is frequently detected in water bodies across the globe. The present study used zebrafish as a model organism to investigate the effects of GAB on the early development of zebrafish and on its antioxidant system. Acute toxicity tests indicated that the 96 h LC₅₀ value of GAB for zebrafish embryos was 59.9 g L⁻¹. Further, it was observed that GAB causes malformation of embryos such as hemagglutination and pericardial edema. Compared to the control group, a significant enhancement (p < 0.05) of heartbeat rates was found at GAB concentrations exceeding 50 mg L⁻¹, while the swimming frequency was clearly increased upon exposure to GAB at a concentration of 100 mg L⁻¹ (p < 0.05). Additionally, the development of the zebrafish embryo was also negatively impacted after exposure to GAB as demonstrated by significantly decreased body lengths. Exposure to GAB at concentrations exceeding 50 mg L⁻¹ significantly influenced the development of zebrafish, leading to malformation of organs and abnormal movements. Although no significant developmental effects of GAB were observed at environmentally relevant concentrations (0.1 and 10 μg L⁻¹), further research about the antioxidant system confirmed that severe oxidant injury happened inside the organisms. catalase (CAT), lactate dehydrogenase (LDH), glutathione S-transferase (GST), glutathione (GSH) and the ability of inhibition of hydroxyl radicals (IHR) were used as biomarkers in the present study to illustrate GAB toxicity at environmentally relevant concentrations. The results showed that activities of CAT, LDH and GST as well as IHR were all elevated after GAB exposure, which proved that ROS were formed in the body as derived from GAB exposure. Among all of these biomarkers, CAT was the most sensitive one to evaluate the influence of GAB, and showed a significant increase even at a very low exposure concentration (0.1 μg L⁻¹).